1. Field of the Invention
The present invention relates to a bend-shaping press mold used for bend-shaping a glass plate to have a convex surface and a concave surface on each side in a heating furnace, a method of bend-shaping a glass plate into a shape having a curved surface as described above, and an apparatus used for carrying out the above-mentioned method.
2. Technical Considerations
Various kinds of curved glass plates are used as elements for transportation means such as automobiles, trains, ships, aircrafts, buildings and so on. Various methods of bending glass plates have been used. As a typical method, a glass plate is cut to have a predetermined dimensions; the glass plate is heated to a glass softening temperature or a temperature close to it, and the glass plate is bent by using a press-forming method, a deadweight forming method or an air-forming method.
Recently, as a large variety of designs are employed for automobiles, there is a demand for windshield glass plates for automobiles such that, for instance, when a glass plate is attached to an automobile, the glass plate has a single arc in the horizontal direction, but in the vertical direction, the major portion of the glass plate is bent in one direction, the remainder being bent in the opposite direction, namely, the glass plate has at least a portion having an S-letter in cross section. In other words, the glass plate has a portion of inflection. It has been proposed to bend a glass plate by using a deadweight bending mold. Generally, a laminated glass wherein two glass plates are laminated and bonded to each other is used for a windshield glass in an automobile. When such a laminated glass is to be prepared, a step of simultaneously bend-shaping two glass plates is needed. The bend-shaping operation for the laminated glass is generally conducted by using a deadweight bend-shaping mold. However, it is difficult to bend-shape glass plates having a convex surface and a concave surface on each side because a portion having a small radius of curvature can not completely follow the shape of the deadweight bending mold.
Therefore, the bending operation to a glass plate having a convex surface and a concave surface at a plane is conducted as follows. A pair of bend shaping press dies having shaping surfaces which are complementary to each other are prepared. A glass plate is heated to a temperature near the softening point of glass; the glass plate is put between the pressing dies after it has been provisionally bent by its own deadweight, if necessary, and the glass plate is press-molded.
In the bend-shaping press mold used for carrying out the above-mentioned method, it is difficult to form the pressing dies having the shaping surfaces with sufficient accuracy so that the pair of pressing dies are simultaneously urged to the glass plate, and there results disagreement in shape of the pair of pressing dies, whereby a part of the glass plates is strongly pressed in pressing operations. A pressing force to a part of the glass plate causes a stress in it. In order to avoid the occurrence of a stress, it is necessary to increase accuracy of the shaping surface of the mold. However, such requirement increases cost for preparing the mold and it is technically difficult to manufacture the mold with high accuracy. Even though a mold having highly accurate shaping surface can be prepared, it is necessary to set a pair of dies at correct positions as well as the positioning of the glass plate, and much labor is required for the positioning.